During the pneumatic insertion of the weft thread, the orifice of the main nozzle should be located as close as possible to the entrance to the channel defined by the teeth of the confiner reed. On the other hand, after the insertion of a pick, it is desirable to engage the thread in the cutting scissors, which requires a certain retraction of the nozzle during the forward movement of the sley. In view of these functional necessities, weft insertion nozzles having a certain mobility have already been designed. Thus, a telescopic nozzle system is known which is controlled through the intermediary of a cable which causes the retraction of the nozzle upon the forward movement of the sley. Nozzles also have been mounted to slide along their axis.